An amperometric glucose biosensor based on glucose oxidase immobilized in electropolymerized poly(o-aminophenol) and carbon nanotubes composite film on a gold electrode.

An amperometric glucose biosensor is developed that is based on immobilization of glucose oxidase (GOD) in a composite film of poly(o-aminophenol) (POAP) and carbon nanotubes (CNT), which are electrochemically co-polymerized at a gold (Au) electrode. Because of the high surface per volume ratio and excellent electrical conductivity of CNT, the biosensor based on an Au/POAP/CNT/GOD electrode has lower detection limit (0.01 mM), larger maximum response current (0.24 mA cm(-2)) and higher sensitivity (11.4 mA M(-1) cm(-2)) than the values of the biosensor based on an Au/POAP/GOD electrode. Additionally, the biosensor shows fast response time, large response current, and good anti-interferent ability for ascorbic acid, uric acid and acetaminophen. Good reproducibility and stability of the biosensor are also observed.     

Amperometric glucose biosensor based on electrodeposition of platinum nanoparticles onto covalently immobilized carbon nanotube electrode

A new amperometric biosensor for glucose was developed based on adsorption of glucose oxidase (GOx) at the gold and platinum nanoparticles-modified carbon nanotube (CNT) electrode. CNTs were covalently immobilized on gold electrode via carbodiimide chemistry by forming amide linkages between carboxylic acid groups on the CNTs and amine residues of cysteamine self-assembled monolayer (SAM). The fabricated GOx/Au_nano/Pt_nano/CNT electrode was covered with a thin layer of Nafion to avoid the loss of GOx in determination and to improve the anti-interferent ability. The immobilization of CNTs on the gold electrode was characterized by quartz crystal microbalance technique. The morphologies of the CNT/gold and Pt_nano/CNT/gold electrodes have been investigated by scanning electron microscopy (SEM), and the electrochemical performance of the gold, CNT/gold, Pt_nano/gold and Pt_nano/CNT/gold electrodes has also been studied by amperometric method. In addition, effects of electrodeposition time of Pt nanoparticles, pH value, applied potential and electroactive interferents on the amperometric response of the sensor were discussed.

The enzyme electrode exhibited excellent electrocatalytic activity and rapid response for glucose in the absence of a mediator. The linear range was from 0.5 to 17.5 mM with correction coefficient of 0.996. The biosensor had good reproducibility and stability for the determination of glucose.     

Enzyme-dispersed carbon-nanotube electrodes: a needle microsensor for monitoring glucose

The preparation of an enzyme-dispersed carbon-nanotube (CNT) electrode, based on mixing glucose oxidase (GOx) within CNT, is described. The new binderless biocomposite was packed within a 21-gauge needle and used for amperometric monitoring of glucose. The resulting microsensor offers a low-potential highly selective and sensitive detection of glucose. The high sensitivity and selectivity are coupled to a wide linear range, prolonged lifetime and oxygen independence. About 80% of the GOx activity is retained during a 24 h thermal stress at 90 degrees C, reflecting the enzyme-stabilization action of CNT. The marked electrocatalytic action towards hydrogen peroxide allows highly selective detection of the glucose substrate at -0.1 V (vs. Ag/AgCl) with no interferences from coexisting ascorbic acid, acetaminophen or uric acid. Linearity prevails up to 40 mM glucose (with analytically useful signals observed up to 0.1 M). Factors affecting the performance of the CNT-based glucose biosensor were assessed and optimized. The attractive performance of the new needle electrode offers great promise for continuous monitoring of glucose in connection to the management of diabetes, and for the biosensing of other metabolites.     

Prussian Blue bulk modified screen-printed electrodes for H(2)O(2) detection and for biosensors

A sensor for H(2)O(2) amperometric detection based on a Prussian Blue (PB) bulk modified carbon screen-printed electrode was developed. It has been optimised with respect to the lowest limit of detection achieved. PB was made chemically by the reaction of FeCl(3) with K(4)[Fe(CN)(6)]. The resulting powder, obtained by forced crystallisation induced by acetone, was dried and activated at 150 degrees C for 10 h. PB microparticles (<38 mum) were prepared and mixed with carbon ink. The limit of detection achieved was 0.4 muM with the linear range up to 100 muM of H(2)O(2) with the sensitivity of 137 muA mM(-1) cm(-2), that was comparable with sensors based on electrodeposited PB film. The transducer was applied for a glucose biosensor, that exhibited LOD of 0.22 mM, linear range up to 3 mM, K(M)(app) of 4.6 mM, and the sensitivity of 3.21+/-0.16 muA mM(-1) cm(-2). The peroxide sensor, as well as the glucose biosensor, were totally insensitive to oxygen, ascorbate, urate, and paracetamol.     

Hydrogen peroxide biosensor with a supramolecular layer-by-layer design

A new sensor design is reported for the construction of an amperometric enzyme biosensor toward H (2)O(2). It was based in the supramolecular immobilization of alternating layers of horseradish peroxidase (either modified with 1-adamantane or beta-cyclodextrin-branched carboxymethylcellulose residues) on Au electrodes coated with polythiolated beta-cyclodextrin polymer. The analytical response of the electrodes, using 1 mM hydroquinone as an electrochemical mediator, increases when the number of enzyme layers increases. The biosensor having three enzyme layers showed a sensitivity of 720 microA/M cm (2) and a detection limit of 2 microM and retained 96% of its initial activity after 30 days of storage. The host-guest supramolecular nature of the immobilization method was confirmed by cyclic voltammetry.     

Sol-gel based amperometric biosensor incorporating an osmium redox polymer as mediator for detection of L-lactate

A novel amperometric biosensor for the determination of lactate was constructed by first immobilizing lactate oxidase and an osmium redox polymer ([Os(bpy)(2)(PVP)(10)Cl]Cl; abbreviated Os-polymer) on the surface of a glassy carbon electrode, followed by coating with a sol-gel film derived from methyltriethoxysilane (MTEOS). The electrooxidation current of this electrode was found to be diffusion controlled. In the presence of lactate, a clear electrocatalytic oxidation wave was observed, and lactate could be determined amperometrically at 400 mV versus Ag AgCl . The concentration range of linear response, slope of linear response and detection limit were 0.1-9 mM, 1.02 microA mM(-1), and 0.05 mM, respectively. Although L-ascorbate was electrooxidized at this potential, uric acid, paracetamol and glucose were found not to interfere.     

Catalytic activity of oxidases hosted in lipidic cubic phases on electrodes

The monoolein-based liquid crystalline cubic phase was used as the matrix to incorporate redox enzymes--glucose (GOx), pyranose (PyOx) oxidases and laccase. Thin layer of the cubic phase embedding GOx or PyOx activated glucose oxidation in the presence and absence of appropriate mediators. The electrodes exhibited unchanged voltammetric response to glucose for not less than six days. The potentials and ratio of catalytic to diffusion currents could be modified by choosing appropriate electroactive probes as mediators. Ferrocenecarboxylic acid and Ru(NH3)6(2+) provided contact between the electrode and the enzyme. The sensitivity to glucose for glucose oxidase was 0.4+/-0.05, 11+/-3.1 microA/cm2/mM without mediator and with ferrocenecarboxylic acid respectively and 0.9+/-0.06, 31+/-5.6 microA/cm2/mM for pyranose oxidase without and with mediator. The system based on glucose oxidase and Ru(NH3)6(2+) as mediator was found useful due to the most negative potential of the process. The catalyses of oxygen reduction by two laccases: Cerrena unicolor and Trametes hirsuta embedded in the cubic phase together with 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonate (ABTS) as the mediator were found efficient and the reduction potential was positive enough to be considered in the application of lyotropic liquid crystals as a material for biofuel cells.     

Quantitative determinations of SiC and SiO2 in new ceramic materials by Fourier transform infrared spectroscopy

In this paper, we have critically evaluated the electrochemical behavior of the products of seven substrates of the enzyme label, alkaline phosphate, commonly used in electrochemical immunosensors. These products (and the corresponding substrates) include indigo carmine (3-indoyl phosphate), hydroquinone (hydroquinone diphosphate), 4-nitrophenol (4-nitrophenol phosphate), 4-aminophenol (p-aminophenyl phosphate), 1-naphthol (1-naphthyl phosphate), phenol (phenyl phosphate), and L-ascorbic acid (2-phospho-L-ascorbic acid). Cyclic voltammetry and amperometry of these products were carried out at glassy carbon (GC), screen-printed carbon (SPC) and gold (Au) electrodes, respectively. Among the products, L-ascorbic acid showed the most sensitive (24.8 microA cm(-2), 12.0 microA cm(-2), and 48.0 microA cm(-2) of 100 microM ascorbic acid at GC, SPC, and Au electrodes, respectively) and well-defined amperometric response at all electrodes used, making 2-phospho-l-ascorbic acid the best substrate in electrochemical detection involving an alkaline phosphatase (ALP) enzyme label. The 2-phospho-L-ascorbic acid is also commercially available and inexpensive. Therefore, it was the best choice for electrochemical detection using ALP as label. Using mouse IgG as a model, an ALP enzyme-amplified sandwich-type amperometric immunosensor was constructed. The immunosensor was designed by electropolymerization of o-aminobenzoic acid (o-ABA) conductive polymer on the surface of GC, SPC, and Au electrodes. The anti-mouse IgG was subsequently attached on the electrode surface through covalent bonding between IgG antibody and the carboxyl groups from poly(o-ABA). Using 2-phospho-L-ascorbic acid as a substrate, the poly(o-ABA)/Au immunosensor produced the best signal (about 297 times of current density response ratio between 1000 ng mL(-1) and 0 ng mL(-1) of mouse IgG), demonstrating that amperometric immunosensors based on a conducting polymer electrode system were sensitive to concentrations of the mouse IgG down to 1 ng mL(-1), with a linear range of 3-200 ng mL(-1) (S.D.<2; n=3), and very low non-specific adsorption.     

Electrochemical biosensors based on redox carbon nanotubes prepared by noncovalent functionalization with 1,10-phenanthroline-5,6-dione

To improve the electrocatalytic activities of carbon nanotubes (CNT) towards the oxidation of nicotinamide adenine dinucleotide (NADH), we derive them with a redox mediator, 1,10-phenanthroline-5,6-dione (PD), by the noncovalent functionalization method. The redox carbon nanotubes (PD/CNT/GC) show excellent electrocatalytic activities towards the oxidation of NADH (catalytic reaction rate constant, k(h) = 7.26 × 10(3) M(-1) s(-1)), so the determination of NADH can be achieved with a high sensitivity of 8.77 μA mM(-1) under the potential of 0.0 V with minimal interference. We also develop an amperometric ethanol biosensor by integration of alcohol dehydrogenase (ADH) within the redox carbon nanotubes (PD/CNT/GC). The ethanol biosensor exhibits a wide linear range up to 7 mM with a lower detection limit of 0.30 mM as well as a high sensitivity of 10.85 nA mM(-1).     

Enzyme-free amperometric sensing of glucose by using gold nanoparticles

A nonenzymatic electrochemical method is described for the detection of glucose by using gold (Au) nanoparticles self-assembled on a three-dimensional (3D) silicate network obtained by using sol-gel processes. The nanosized Au particles have been self-assembled on the thiol tail groups of the silicate network and enlarged by hydroxylamine. The Au nanoparticles efficiently catalyze the oxidation of glucose at less-positive potential (0.16 V) in phosphate buffer solution (pH 9.2) in the absence of any enzymes or redox mediators. The Au nanoparticle-modified transducer (MPTS-nAuE) was successfully used for the amperometric sensing of glucose and it showed excellent sensitivity with a detection limit of 50 nM. The common interfering agent ascorbate (AA) does not interfere with the detection of glucose. The MPTS-nAuE transducer showed individual voltammetric responses for glucose and AA. This transducer responded linearly to glucose in the range of 0-8 mM and the sensitivity of the transducer was found to be 0.179 nA cm(-2) nM(-1). Excellent reproducibility, and long-term storage and operational stability was observed for this transducer.     

Direct electrochemistry of glucose oxidase in a colloid Au-dihexadecylphosphate composite film and its application to develop a glucose biosensor

Colloid Au (Au(nano)) with a diameter of about 10 nm was prepared and used in combination with dihexadecylphosphate (DHP) to immobilize glucose oxidase (GOD) onto the surface of a graphite electrode (GE). The direct electrochemistry of GOD confined in the composite film was investigated. The immobilized GOD displayed a pair of redox peaks with a formal potential of -0.475 mV in pH 7.0 O(2)-free phosphate buffers at scan rate of 150 mV s(-1). The GOD in the composite film retained its bioactivity and could catalyze the reduction of dissolved oxygen. Upon the addition of glucose, the reduction peak current of dissolved oxygen decreased, which could be developed for glucose determination. A calibration linear range of glucose was 0.5-9.3 mM with a detection limit of 0.1 mM and a sensitivity of 1.14 microA mM(-1). The glucose biosensor showed good reproducibility and stability. The general interferences that coexisted in human serum sample such as ascorbic acid and uric acid did not affect glucose determination.     

Functional groups modulate the sensitivity and electron transfer kinetics of neurochemicals at carbon nanotube modified microelectrodes

The surface properties of carbon-based electrodes are critically important for the detection of biomolecules and can modulate electrostatic interactions, adsorption and electrocatalysis. Carbon nanotube (CNT) modified electrodes have previously been shown to have increased oxidative sensitivity and reduced overpotential for catecholamine neurotransmitters, but the effect of surface functionalities on these properties has not been characterized. In this study, we modified carbon-fiber microelectrodes (CFMEs) with three differently functionalized single-wall carbon nanotubes and measured their response to serotonin, dopamine, and ascorbic acid using fast-scan cyclic voltammetry. Both carboxylic acid functionalized and amide functionalized CNTs increased the oxidative current of CFMEs by approximately 2-6 fold for the cationic neurotransmitters serotonin and dopamine, but octadecylamine functionalized CNTs resulted in no significant signal change. Similarly, electron transfer was faster for both amide and carboxylic acid functionalized CNT modified electrodes but slower for octadecylamine CNT modified electrodes. Oxidation of ascorbic acid was only increased with carboxylic acid functionalized CNTs although all CNT-modified electrodes showed a trend towards increased reversibility for ascorbic acid. Carboxylic acid-CNT modified disk electrodes were then tested for detection of serotonin in the ventral nerve cord of a Drosophila melanogaster larva, and the increase in sensitivity was maintained in biological tissue. The functional groups of CNTs therefore modulate the electrochemical properties, and the increase in sensitivity from CNT modification facilitates measurements in biological samples.     

A promising dehydrogenase-based bioanode for a glucose biosensor and glucose/O2 biofuel cell

A new type of dehydrogenase-based amperometric glucose biosensor was constructed using glucose dehydrogenase (GDH) which was immobilized on the edge-plane pyrolytic graphite (EPPG) electrode modified with poly(phenosafranin)-functionalized single-walled carbon nanotubes (PPS-SWCNTs). The PPS-SWCNT-modified EPPG electrode was prepared by electropolymerization of phenosafranin on the EPPG electrode which had been previously coated with SWCNTs. The performance of the GDH/PPS-SWCNT/EPPG bioanode was evaluated using cyclic voltammetry and amperometry in the presence of glucose. The GDH/PPS-SWCNT/EPPG electrode possesses promising characteristics as a glucose sensor: a wide linear dynamic range of 50 to 700 μM, low detection limit of 0.3 μM, fast response time (1-2 s), high sensitivity (96.5 μA cm(-2) mM(-1)), and anti-interference and anti-fouling abilities. Moreover, the performance of the GDH/PPS-SWCNT/EPPG bioanode was tested in a glucose/O(2) biofuel cell. The maximum power density delivered by the assembled glucose/O(2) biofuel cell could reach 64.0 μW cm(-2) at a cell voltage of 0.3 V with 40 mM glucose.     

Measurement of binding kinetics between PI3-K and phosphorylated IGF-1R using a surface plasmon resonance biosensor

A high-performance amperometric glucose biosensor was developed, based on immobilization of glucose oxidase (GOx) on a copper (Cu) nanoparticles/chitosan (CHIT)/carbon nanotube (CNT)-modified glassy carbon (GC) electrode. The Cu and CNT had a synergistic electrocatalytic effect toward the reduction of hydrogen peroxide in the matrix of biopolymer CHIT. The Cu/CHIT/CNT modified GC electrode could amplify the reduction current of hydrogen peroxide greatly. Besides, the Cu/CHIT/CNT modified GC electrode reduces hydrogen peroxide at a much lower applied potential and inhibit the responses of interferents. With GOx as an enzyme model, a new glucose biosensor was fabricated. The sensitivity of the sensor is due not only to the large microscopic area but also to the high efficiency of transformation of H₂O₂ generated by enzymatic reaction to current signal. The biosensor exhibited excellent sensitivity (the detection limit is down to 0.02 mM), fast response time (less than 4 sec), wide linear range (from 0.05 to 12 mM), and perfect selectivity. Correspondence: Wanzhi Wei, State key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China     

Hydrogen peroxide and glucose biosensor based on silver nanowires synthesized by polyol process

Silver nanowires synthesized through a polyol process using polyvinylpyrrolidone as protection (PVP-AgNWs) were used as a new electrode material for constructing a sensor. Hydrogen peroxide (H(2)O(2)) and glucose were used as analytes to demonstrate the sensor performance of the PVP-AgNWs. It is found that the PVP-AgNWs-modified glassy carbon electrode (PVP-AgNWs/GCE) exhibits remarkable catalytic performance toward H(2)O(2) reduction. This sensor has a fast amperometric response time of less than 2 s and the catalytic current is linear over the concentration of H(2)O(2) ranging from 20 μM to 3.62 mM (R = 0.998) with a detection limit of 2.3 μM estimated on a signal-to-noise ratio of 3. A glucose biosensor was constructed by immobilizing glucose oxidase (GOD) onto the surface of the PVP-AgNWs/GCE. The resultant glucose biosensor can be used for glucose detection in human blood serum with a sensitivity of 15.86 μA mM(-1) cm(-2) and good selectivity and stability.     

Effects of electrolyte and pH on the behavior of cross-linked films of ferrocene-modified poly(ethylenimine)

Ferrocene redox polymers based on the coupling of ferrocenecarboxaldehyde to both linear and branched poly(ethylenimine) (PEI) have been prepared to investigate the effects of pH, electrolyte, and cross-linking on electron charge transport and film swelling. The redox behavior of both ferrocene-modified linear PEI and ferrocene-modified branched PEI was investigated by cyclic voltammetry, while electron diffusion coefficients reported for PEI-based redox polymers were determined by electrochemical impedance spectroscopy. In phosphate solutions at pH>7, cross-linked films of both redox polymers exhibited multiple redox wave behavior and were unstable. In contrast, in non-phosphate solutions, cross-linked films exhibited stable electrochemical behavior and fast electron transfer in solutions with pH<11. Gel swelling experiments suggested that the multiple wave behavior and instability exhibited in either phosphate solutions or at high pH in non-phosphate solutions were related to a combination of film collapse and electrolyte binding within the hydrogel. The electron diffusion coefficients for these polymers are on the order of 10-8 (mol cm(-2) s(-1/2)), which are approximately 40 times greater than other ferrocene-modified polymers. Incorporation of the enzyme, glucose oxidase, into these films demonstrated that these redox polymers were able to electrically communicate with the enzyme's flavin adenine dinucleotide (FAD) redox centers. Glucose sensors based on these films exhibited enzyme saturation current densities that ranged from 240 to 480 microA/cm2 in response to glucose, which were dependent upon the supporting electrolyte and pH. The sensitivity of these sensors at 5 mM glucose ranged from 10 to 48 microA.cm(-2).mM(-1).     

Self-gelatinizable copolymer immobilized glucose biosensor based on prussian blue modified graphite electrode

A novel poly(vinyl alcohol) grafting 4-vinylpyridine self-gelatinizable copolymer was adapted to immobilize glucose oxidase. The reduction of hydrogen peroxide (H2O2) was detected at a Prussian Blue (PB) modified graphite electrode. A stable and sensitive glucose amperometric biosensor is described. The copolymer is a good biocompatible polymer in which the glucose oxidase retains high activity. Moreover, the copolymer can adhere firmly to the inorganic PB membrane. The sensor showed an apparent Michaelis-Menten constant of 18 +/- 0.2 mM and a maximum current density of 1.14 microA cm-2 mM-1. The linear range is from 5 microM to 4.5 mM glucose and the detection limit is 0.5 microM glucose. The catalytic efficiency of PB for the reduction of H2O2 is higher than that for the oxidation of H2O2. Glucose concentrations in serum samples from healthy persons and diabetic patients were determined using the sensor. The results compared well with those provided by the hospital using a spectroscopy method.     

Glucose biosensors based on platinum nanoparticles-deposited carbon nanotubes in sol-gel chitosan/silica hybrid

A new strategy for fabricating a sensitivity-enhanced glucose biosensor was presented, based on multi-walled carbon nanotubes (CNT), Pt nanoparticles (PtNP) and sol-gel of chitosan (CS)/silica organic-inorganic hybrid composite. PtNP-CS solution was synthesized through the reduction of PtCl(6)(2-) by NaBH(4) at room temperature. Benefited from the amino groups of CS, a stable PtNP gel was obtained, and a CNT-PtNP-CS solution was prepared by dispersing CNT functionalized with carboxylic groups in PtNP-CS solution. The CS/silica hybrid sol-gel was produced by mixing methyltrimethoxysilane (MTOS) with the CNT-PtNP-CS solution. Then, with the immobilization of glucose oxidase (GOD) into the sol-gel, the glucose biosensor of GOD-CNT-PtNP-CS-MTOS-GCE was fabricated. The properties of resulting glucose biosensor were measured by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). In phosphate buffer solutions (PBS, pH 6.8), nearly interference free determination of glucose was realized at low applied potential of 0.1V, with a wide linear range of 1.2x10(-6) to 6.0x10(-3)M, low detection limit of 3.0x10(-7)M, high sensitivity of 2.08microA mM(-1), and a fast response time (within 5s). The results showed that the biosensor provided the high synergistic electrocatalytic action, and exhibited good reproducibility, long-term stability. Subsequently, the novel biosensor was applied for the determination of glucose in human serum sample, and good recovery was obtained (in the range of 95-104%).     

Facile preparation of carbon nanotube/poly(ethyl 2-cyanoacrylate) composite electrode by water-vapor-initiated polymerization for enhanced amperometric detection

A carbon nanotube/poly(ethyl 2-cyanoacrylate) (CNT/PECA) composite electrode was developed for enhanced amperometric detection. The composite electrode was fabricated on the basis of water-vapor-initiated polymerization of a mixture of CNTs and ethyl 2-cyanoacrylate in the bore of a piece of fused silica capillary. The morphology and structure of the composite were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. The results indicate that the CNTs were well dispersed and embedded throughout the PECA matrix to form an interconnected CNT network. The analytical performance of this unique CNT-based detector has been demonstrated by separating and detecting six flavones in combination with capillary electrophoresis. The advantages of the CNT/PECA composite detector include lower operating potential, higher sensitivity, low expense of fabrication, satisfactory resistance to surface fouling, and enhanced stability; these properties indicate great promise for a wide range of applications.     

Direct Electrochemistry of Glucose Oxidase at Carbon Nanotube‐gold Colloid Modified Electrode with Poly(diallyldimethylammonium chloride) Coating

Glucose oxidase showed direct electrochemical transfer at glassy carbon electrodes immobilized with carbon nanotube‐gold colloid (CNT‐Au) composites with poly(diallydimethylammonium chloride) (PDDA) coatings. The modified electrode (GC/CNT/Au/PDDA‐GOD) was employed for the amperometric determination of glucose. Under optimal conditions, the biosensor displayed linear response to glucose from 0.5 to 5 mM with a sensitivity of 2.50 mA M^?1 at an applied potential of ?0.3 V (vs. Ag|AgCl reference).